skeletal muscle anatomy

functions of muscle

• movement

• maintaining posture

• stabilizing joints

• generating heat

irritability

muscle’s ability to receive and respond to a stimulus

contractility

ability to shorten when stimulated

extensibility

ability to be stretched or extended

elasticity

ability of a muscle fiber to recoil and resume its resting length after being stretched

epimysium

dense irregular connective tissue surrounding the muscle

perimysium

surrounds each fascicle

endomysium

connective tissue that surrounds muscle fibers within a fascicle

muscle fascicle

bundle of muscle fibers

muscle fiber

individual muscle cells

myofibrils

contractile organelle found in a muscle fiber

two types of myofilaments

thick myosin filaments and thin actin filament

thick myosin filaments

myosin proteins that has a head and a tail

thin actin filament

includes actin, tropomyosin, and troponin complex

t-tubule

sections of a sarcolemma that penetrate into the muscle fiber interior

sarcolemma

plasma membrane of a muscle fiber

sarcoplasmic reticulum

smooth endoplasmic reticulum that stores calcium

sarcomere

repeating pattern of thick and thin filaments

z-lines/discs

protein bands that mark the boundary between sarcomeres

m-line

marks the middle of thick myosin filament/sarcomere

a-band

areas in a myofibril that contains overlapping thin and thick myosin filaments

which band is the dark band

a-band because it contains thick myosin filaments

i-band

areas in a myofibril that contains thin actin filaments

which band is the light band

i-band because it contains thin actin filaments

h-band/zone

region of an a-band that contains thick myosin filaments

titin

connects the thick filament to the z-line/disc

where are the tails and heads of a myosin protein found in a thick myosin filament

heads poke up all around the filament and tails form the core of a thick filament

g-actin

most common in a thin myosin filament that look like a string of beads

tropomyosin

ropes that spiral around the G-actin

troponin complex

made up of 3 pieces that connect together and hangs off the tropomyosin

changes that occur during skeletal muscle contraction

• sarcomere shortens

• i-band shortens

• h-zone shortens

• a-band doesn’t change length